Compositions for plants containing phosphonate and phosphate salts, and derivatives thereof

ABSTRACT

A fungicidal composition for plants containing phosphonate (PO 3 ) and phosphate (PO 4 ) salts, and derivatives thereof is disclosed. The composition provides a single product which may be employed to control a  Phytophthora infestans infection in plants.

[0001] The following application is a continuation-in-part of patentapplication Ser. No. 09/109,139, which is a divisional of U.S. Pat. No.5,800,837, which is a continuation-in-part of U.S. Pat. No. 5,736,164.

FIELD OF INVENTION

[0002] The present invention relates to compositions, and methods ofuse, which provide improved efficacy in controlling Phytophthorainfections in plants. More particularly, the composition is comprised ofan amount of phosphate (PO₄) and phosphonate (PO₃), with application ofsuch composition particularly useful in lowering the occurrences of lateblight.

BACKGROUND OF INVENTION

[0003] From 1845 to 1846, the Irish Potato Famine occurred, which wasone of the most devastating crop failures in the history of the world.The potato famine was caused by the disease late blight which resultedin harvested potatoes quickly decaying, making them unsuitable forconsumption. The disease is also known to cause defoliation in infectedplants. Late blight is caused by a Phytophthora organism infecting apotato or tomato plant. As can be gathered, the Phytophthora organism,if not controlled, can cause major economic damage to agriculturalcrops, with the resulting damage causing the loss of millions of dollarsin crop revenues. Additionally, there is the possibility of significantreduction of the potato and tomato supply available to consumers.

[0004] To control late blight, it has been recommended that thecontaminated potatoes and/or tomatoes be buried in deep pits and coveredby at least two feet of soil. In Northern Latitudes, the potatoes ortomatoes can be spread on the soil surface and allowed to freeze duringthe winter. These methods temporarily prevent the spread of the disease,but do not prevent infection and attack by the Phytophthora infestans.The treatment only addresses plants and crops after they have beendestroyed. For this reason, it is desired to have a composition ormethod that can be administered to potato and tomato fields to activelycontrol and prevent the spread of the Phytophthora infestansinfestation.

[0005] Some species of the Phytophthora genus can be controlled, such asPhytophthora parasitica. In particular, fosetyl-al (ethyl phosphonate)can be administered to plants to control diseases such as root rotcaused by Phytophthora parasitica. As such, it is known that manyphosphonate (PO₃) compositions are highly effective in combating thedisease root rot and, in particular, some of the species of the genusPhytophthora. Unfortunately, fosetyl-al and other phosphonates, alone,do not control late blight and similar Phytophthora diseases caused bythe species Phytophthora sojae. Thus, it is desired to have a method orcomposition that readily inhibits infection by and proliferation ofPhytophthora infestans.

[0006] Phosphorus is an essential element in plant nutrition because itgoverns the energy producing reactions, including those that areoxidative and photo phosphorylative. Phosphorous is essential to theproduction of adenosine diphosphate (ADP) and adenosine triphosphate(ATP). Energy-rich phosphate bonds of ADP and ATP provide the energy formany of the physiological reactions that occur in plants. As such,various forms of phosphorous are absorbed by plants for use as part ofthe photosynthetic process.

[0007] The element phosphorous appears in numerous general forms,including phosphonate (PO₃) and phosphate (PO₄). The term “phosphonate,”sometimes also referred to as “phosphite,” means the salts (organic orinorganic) of either phosphonic acid or phosphorous acid. Phosphonic andphosphorous acids have the formula H₃PO₃ and a molecular weight of82.00. Their structures from the International Union of Pure and AppliedChemistry are shown below:

[0008] The term “phosphate” means the salts (organic or inorganic) ofphosphoric acid having the formula H₃PO₄, molecular weight of 98.00 andhaving the following structure:

[0009] In the past, various phosphonate compounds have been proposed asuseful in fungicidal and fertilizer compositions for application toplants. See, e.g. U.S. Pat. Nos. 4,075,324 and 4,119,724 to Thizy,describing phosphorous acid, its inorganic and organic salts, as a plantfungicide; U.S. Pat. No. 4,139,616 to Dueret, describing fungicidalcompositions based on phosphorous acid esters and salts thereof; U.S.Pat. No. 4,542,023 to Lacroix et al., describing organophosphorousderivatives as possessing systemic and contact fangistatic andfungicidal activity; U.S. Pat. Nos. 4,698,334, 4,806,445, and 5,169,646to Horriere et al., describing fungicidal compositions based on alkylphosphonates; U.S. Pat. Nos. 4,935,410 and 5,070,083 to Barlet,describing fungicidal aluminum tris-alkyl-phosphonate compositions; andU.S. Pat. No. 5,514,200 to Lovatt, describing formulations ofphosphorous-containing acid fertilizer for plants. (The teachings of theproceeding U.S. Patents are hereby incorporated by reference.) The abovereferences, disclosing phosphonate compositions, have been found to beeffective for protecting plants and, particularly, grape vines, citrusand fruit trees, and tropical plants against fungal attack.

[0010] Note that phosphonate (PO₃) alone is typically considered anunacceptable source of phosphorus (P) for plants. It is known that PO₃must be converted to PO₄ to be utilized by a plant.

[0011] Once assimilated, phosphonates (PO₃) have been shown to enhancethe plant's phytoimmune system. The phosphonate induced stimulation ofthe phytoimmune system is triggered by the induction of ethyleneproduction, followed by a rapid accumulation of phytoalexins at the siteof infection. Phytoalexins are antibiotics which result from theinteraction between the host plant and a pathogen. The phytoalexins aresynthesized by and accumulate in the plant to inhibit the pathogen. Thephytoalexins will accumulate at the site of an infection to preventfurther spread of the disease, thereby reducing symptomatic expressionof the disease.

[0012] In the past, phosphates (PO₄) were not viewed as a solution topathological acerbation of fungal infections or infections produced byother genuses. This is because phosphates (PO₄) are viewed primarily asa fertilizer with only limited, or even detrimental, phytoimmuneproperties. For example, U.S. Pat. No. 5,514,200 teaches that phosphatefertilizers inhibit beneficial symbiosis between plant roots andmycorrhizal fungi, and further promote bacterial and fungical growth inthe rhizosphere, including the growth of pathogenic fungi and othersmall soil-borne organisms. (Col. 2, lines 18-28). Phosphates (PO₄) havealso been considered to be a competitive inhibitor for phosphonateassimilation, thus inhibiting the ability of phosphonates (PO₃) toprotect against fungus attack. See, Pegg, K. G. and deBoer, R. F.,“Proceedings of the Phosphonic (Phosphorous) Acid Work Shop,”Australiasian Plant Pathology, Vol. 19 (4), pp. 117 and 144, 1990. Yetfurther, phosphonates (PO₃) and phosphates (PO₄) were believed to be“biological strangers,” with the presence of phosphonates (PO₃) oresters of phosphonates, exerting little or no influence on enzymereactions involving phosphates. Robertson, H. E. and Boyer, P. D., “TheBiological Inactivity of Glucose 6—phosphonate (PO₃), InorganicPhosphites and Other Phosphites,” Archives of Biochemistry andBiophysics, 62 pp. 380-395 (1956).

[0013] Accordingly, the requirements for a successful phosphonate-basedfungicide depend on the promotion of the phosphonate-inducedpathological acerbation of fungical or other genus infections. Moreparticularly, it is desired to have a composition and/or method thatprevents Phytophthora infestans infection and destruction of plants.

SUMMARY OF INVENTION

[0014] The present invention relates to compositions and methods for usein preventing infection by and manifestations of the genus Phytophthoraand, more particularly, Phytophthora infestans. The composition will becomprised of phosphate (PO₄) and phosphonate (PO₃) constituents which,when combined, provide for a synergistic effect that results in thesubstantial protection against infection of plants by Phytophthora,especially Phytophthora infestans. As such, the phosphate andphosphonate constituents can be combined to form a composition, whichcan be applied to plants, especially tomatoes and potatoes, to preventinfection by Phytophthora infestans and diseases caused by suchinfection. Application can be achieved by using either a dry mix or anaqueous solution.

[0015] The preferred composition for preventing Phytophthora will becomprised of potassium phosphonate and potassium phosphate, as it hasbeen found that these two constituents, when combined, will cause asynergistic effect which results in the substantial prevention ofinfection by Phytophthora. It is believed, that the rate by whichinfection is prevented is increased by at least 100% when the twoconstituents are combined, as compared to the additive effect of thecombined salts. The two constituents will be combined in an amountsufficient to prevent infection and manifestation by various diseasecausing organisms, with the particular amounts combined dependent uponthe particular species of plant to be treated, the specific diseasecausing organism to be treated, and the particular phosphate salt andphosphonate salt that will be combined.

[0016] The composition should be applied at least once to the plants tobe treated. While one application is sufficient, it is typicallypreferred to make multiple applications. Essentially, any plant infectedby Phytophthora can be treated, with it most preferred to apply thecomposition to potato and tomato plants. It should also be noted thatthe composition not only inhibits Phytophthora, but is environmentallysafe, inexpensive to use, and has low mammalian toxicity.

[0017] Preferably, the composition will contain as an active material aneffective amount of at least a first salt formula selected from thegroup consisting of KH₂PO₃, K₂HPO3, and K₃PO₃, and at least a secondsalt selected from the group consisting of KH₂PO₄, K₂HPO₄, and K₃PO₄, ina mixture with an agriculturally acceptable carrier. The compositionpreferably comprises an aqueous solution wherein each salt is present insolution from about 20 millimole to about 5% vol./vol. Alternatively,and more preferably, the actual volume by use will equal 21.7% by weightPO₄ and 21.5% by weight PO₃. Such composition can then be diluted tobetween 2% and 4% by volume. Importantly, the PO₃ and PO₄ must remainsoluble, meaning not too much PO₃ and PO₄ can be added, otherwise thePO₃ and PO₄ will precipitate.

[0018] Phosphonate salts useful in the practice of the invention alsoinclude those organic and inorganic salts taught by U.S. Pat. Nos.4,075,324 and 4,119,724 to Thizy et al., (see, e.g., col. 1, In. 51-69through col. 2, In. 1-4).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0019] The present invention relates to compositions and methods for usein preventing diseases, such as late blight, caused by the genusPhytophthora. In particular, the present invention relates tocompositions and methods for use in preventing plant diseases caused byPhytophthora infestans. The composition is comprised of a phosphate(PO₄) constituent and phosphonate (PO₃) constituent, with it mostpreferred that a composition comprised of potassium phosphonate andpotassium phosphate be used. Once the composition is formed, it can beapplied to plants to prevent infection by Phytophthora infestans andmanifestations related to the infection. The composition can be appliedas either a dry mix or an aqueous solution to plants prior to infectionby the Phytophthora infestans organism.

[0020] The composition for preventing Phytophthora infestans is preparedby combining phosphonate and phosphate constituents. Any of a variety ofphosphates are suitable for use, including K₂HPO₄, K₃PO₄, KH₂PO₄,(NH₃)₂HPO₄, (NH₃) H₂PO₄, and combinations thereof. The phosphonates,like the phosphates, can be selected from any of a variety ofcompositions, including K₂HPO₃, K₂PO₃, KH₂PO₃ (NH₃)₂HPO₃, (NH₃) H₂PO₃,and combinations thereof. Any phosphate and phosphonate constituentcombination can be used as long as infection by and manifestation ofPhytophthora infestations is inhibited. Additionally, it is necessaryfor the constituents to have suitable solubility in a carrier and to beof a constitution to allow easy distribution in an area where plants tobe treated are grown. More preferably, the phosphonate and phosphateconstituents, when combined, will have a synergistic effect ininhibiting Phytophthora infestans. The most preferred phosphate (PO₄)and phosphonate (PO₃) constituents for use in preventing Phytophthorainfestans infection are combinations of K₂HPO₃ and K₂HPO₄. As such, thephosphate (PO₄) and phosphonate (PO₃) constituents are combined to formthe composition used to prevent Phytophthora infestans infection.

[0021] While the discussed constituents are preferred for use intreating plants and preventing infection by the Phytophthora organism,variations of the phosphate and phosphonate constituents can be used. Assuch, it is preferred if the compound comprises a fungicidally effectiveamount of at least a first salt having the following formula:

[0022] and a second salt having the following formula:

[0023] where R₁ is selected from the group consisting of H, K, an alkylradical containing from 1 to 4 carbon atoms, halogen-substituted alkylor nitro-substituted alkyl radical, an alkenyl, halogen-substitutedalkenyl, alkynl, halogen-substituted alkynl, alkoxy-substituted alkylradical, ammonium substituted by alkyl and hydroxy alkyl radicals;

[0024] R₂ and R₃ are selected from a group consisting of H and K;

[0025] Me is selected from a group consisting of K, alkaline earth metalcations, aluminum atom, and the ammonium cation; and

[0026] n is a whole number from 1 to 3, equal to the valence of Me.

[0027] Optionally, the second salt can be of the formula:

[0028] with the above listed formula constituents still applicable.

[0029] The constituents should be preferably mixed with a suitablecarrier to facilitate distribution to an area where the plants to betreated are grown. The carrier should be agriculturally acceptable, withwater (H₂O) most preferred.

[0030] As an example of how to form the composition, it is preferred tofirst form a potassium phosphonate aqueous solution, with thephosphonate formation as follows:

[0031] H₃PO₃ is produced by the hydrolysis of phosphorus trichlorideaccording to the reaction: PCl₃+3H₂O>H₃PO₃+3HCl. The HCl is removed bystripping under reduced pressure, and the phosphonic acid (H₃PO₃) issold as a 70% acid solution.

[0032] The phosphonic acid is then neutralized in aqueous solution bypotassium hydroxide according to the reaction: H₃PO₃+KOH>KH₂PO₃+H₂O toabout pH 6.5, and to produce a 0-22-20 liquid weighing 11.15 lbs./gal.This solution is commercially available and is sold under the trademark“Phos-Might” by Foliar Nutrients, Inc., Cairo, Ga. 31728.

[0033] The phosphate (PO₄) is produced by reacting mono potassiumphosphate (0-51.5-34) with 45% potassium hydroxide in aqueous solutionto produce dipotassium phosphate, by the following reaction:KH₂PO₄+KOH>K₂HPO₄+H₂O with a product density of 1.394 at 20° C. and asolution pH of 7.6 producing a 0-18-20 analysis. This solution iscommercially available and is sold under trademark “K-Phos” by FoliarNutrients, Inc., Cairo, Ga. 31724.

[0034] After the potassium phosphonate and potassium phosphateconstituents, or other phosphonate and phosphate constituents, areformed, they can be combined to produce the potassium phosphonate andpotassium phosphate composition. This composition is used to then treatplants for the prevention of infection by the Phytophthora genus,especially Phytophthora infestans.

[0035] Varying amounts of each compound, for example, K₂HPO₃, KH₂PO₃,K₂HPO₄, or KH₂PO₄ in an aqueous solution, are combined at rates rangingfrom 20 millimole to 5% vol./vol., depending on crop host and thepathogen complex and level of infection. Alternatively, the amount ofthe first salt is equal to one part by weight and the amount of thesecond salt is equal to between 0.001 and 1,000 parts by weight. It ispreferred if the composition is comprised of 21.7% K₂HPO₄ and 21.5%K₂HPO₃ or 11.8% PO₄ ⁻³ and 10.7% PO3⁻², all of which are soluble.

[0036] Once formed, the composition will be applied to various plants toprevent Phytophthora infestans infection. The preferable method ofapplication is foliar, either by ground or aerial equipment, but is notlimited to that method alone. Injection or soil applications, forexample, could also be efficacious depending on specific crops andpathogens. While it is preferred to apply the composition in an aqueoussolution, other forms of application may be used, including dusts,flowables, water dispersable granules, granules and inert emulsions, aswell as oils. At least one application should be made; however, multipleapplications of the composition can be made.

[0037] The inventive composition has utility on fruit crops, agronomiccrops, ornamentals, trees, grasses, vegetables, grains, andfloricultural crops, as well as some aquatic crops, including watercress. The crops most likely infected by Phytophthora infestans arepotatoes (Solanum tuberosum) and tomatoes (Lycopersicon esculentum). Assuch, the present composition is especially useful in treating potatoand tomato plants to prevent Phytophthora infection.

[0038] The following examples set forth the preferred concentrations andtechniques for formulation thereof, as well as methods of application,use and test results demonstrating the efficacy of the inventiveconcentration in protecting plants against attack by Phytophthorainfestans. It is to be understood, however, that these Examples arepresented by way of illustration only, and nothing therein shall betaken as a limitation upon the overall scope of the invention. Thespecific components tested in the Examples were prepared and applied asfollows.

[0039] In each of Examples 1 and 2, treatments were applied as a onegallon solution by a back pack sprayer, maintained at about 60 psi, insufficient quantities of water to achieve thorough coverage. Alltreatments were applied to the appropriate number of experimental unitsassigned in a randomized complete block (CRB) design replicated fourtimes.

[0040] As used in the examples, “Percent Late Blight” means the percentof plants that exhibit blight. “Lesions Per Plant” relate to the numberof lesions on a particular plant caused by the infectious inoculum. The“No. Infected Leaflets” relates to the number of infected leaves perplant.

EXAMPLES Example 1

[0041] Potatoes (Solanum tuberosum, variation Atlantic) were infectedwith a pathogen, Phytophthora infestans, to determine whether suitabletreatments could be developed to eliminate the pathogen from theinfected plants and, more importantly, prevent infection of the plantsby the pathogen. The Phytophthora pathogen causes late blight ininfected plants. The plants were treated with the below listedcompositions, twice, with the applications being seven (7) days apart.The composition of the inoculant added to the plants is listed below inthe table. One week (7 days) after the last inoculation was made to theplants, the potato plants were then infected with the pathogen,Phytophthora infestans. The infectious inoculum was equal to 12,000sporangia per millimeter (ml), with 20 ml administered per plant. TheGenotype of the pathogen was US-8 and the Matingtype was A2. Seven daysafter inoculation with the pathogen, the results were tabulated todetermine the percentage of blight in the plants and the number oflesions per plant. Additionally, the number of infected leaflets perplant were tabulated. The results are as follows: SUMMARY LATE BLIGHTOBSERVATIONS FNX GREENHOUSE EXPERIMENT NO. INFECTED % LATE LESIONSLEAFLETS TREATMENT RATE/A BLIGHT PER PLANT PER PLANT K₂HPO₃ + 1% + 0.390.5 0.5 K₂HPO₄ 1% Cu-EDDHA 0.2 lb. ai 12.30 35.3 26.9 K₂HPO₃ 1% 1.85 2.41.8 K₂HPO₄ 1% 18.45 41.4 31.1 CONTROL 28.12 84.4 50.1

[0042] As can be seen, an inoculum of just phosphonate (PO₃) showed goodresults in controlling the blight. However, better results were achievedusing the phosphate (PO₄) and phosphonate (PO₃) composition. The (PO₄)and (PO₃) combination demonstrated exceptional blight depression,indicating that potato blight can be better controlled using acomposition comprised of (PO₃) and (PO₄). This indicates that asynergistic effect is achieved with a (PO₃) and (PO₄) combination.

Example 2

[0043] Tomatoes (Lycopersicon esculentum, FL 40) were infected with apathogen, Phytophthora infestans, to determine whether suitabletreatments could be developed to prevent infection of the plants by thepathogen. The Phytophthora pathogen causes late blight in infectedplants. The plants were treated with the below listed compositions,twice, with the application dates being seven (7) days apart. Thecomposition of the inoculant added to the plants is listed below in thetable. One week (7 days) after last inoculation was made to the plants,the tomato plants were then infected with the pathogen, Phytophthorainfestans. The infectious inoculum was equal to 12,000 sporangia permillimeter (ml), with 20 ml administered per plant. The Genotype of thepathogen was US-17 and the Matingtype was A1. Seven days afterinoculation with the pathogen, the results were tabulated to determinethe percentage of blight in the plants and the number of lesions perplant. Additionally, the number of infected leaflets per plant weretabulated. The results are as follows: GREENHOUSE TOMATO LATE BLIGHTTRIAL NO. INFECTED TREATMENT RATE/A LESIONS/PLANT LEAFLETS/PLANTK₂HPO₃ + 2%  6.0  2.5 K₂HPO₄ SIMAZINE 4L 0.1 lb. ai 52.3 36.8 K₂HPO₃ 1%56.7 21.5 K₂HPO₄ 1% 74.8 36.5 CONTROL 66.8 33.8

[0044] Excellent results were achieved using the phosphate (PO₄) andphosphonate (PO₃) composition. The (PO₄) and (PO₃) combinationdemonstrated exceptional blight depression, indicating that the blightcan be better controlled using a composition comprised of (PO₃) and(PO₄). This indicates that a synergistic effect is achieved with a (PO₃)and (PO₄) combination.

[0045] The above Examples demonstrate that the inventive compositionsare useful in protecting plants against attack by the Phytophthorainfestans infection with the application of one solution.

[0046] The disclosures in all references cited herein are incorporatedby reference.

[0047] Alternatively, the composition can be used to prevent infectionby Phycomycetes, Ascomycetes, and other fungal pathogens, as well asbacteria.

[0048] Thus, there has been shown and described a method relating to theuse of a phosphonate (PO₃) and phosphate (PO₄) composition whichprovides improved efficacy in controlling Phytophthora infections inplants which fulfills all the objects and advantages sought therefore.It is apparent to those skilled in the art, however, that many changes,variations, modifications, and other uses and applications for aphosphonate (PO₃) and phosphate (PO₄) composition are possible, and alsosuch changes, variations, modifications, and other uses and applicationsof a phosphonate (PO₃) and phosphate (PO₄) composition which do notdepart from the spirit and scope of the invention are deemed to becovered by the invention, which is limited only by the claims whichfollow.

What is claimed is:
 1. A composition for preventing and controllingdiseases in plants caused by Phytophthora, whereby said compositioncomprises an effective amount of at least a first salt having thefollowing formula:

and a second salt having the following formula:

where R₁ is selected from the group consisting of H, K, an alkyl radicalcontaining from 1 to 4 carbon atoms, halogen-substituted alkyl ornitro-substituted alkyl radical, an alkenyl, halogen-substitutedalkenyl, alkynl, halogen-substituted alkynl, alkoxy-substituted alkylradical, ammonium substituted by alkyl or hydroxy alkyl radicals; R₂ andR₃ are selected from the group consisting of H and K; Me is selectedfrom the group consisting of K, alkaline earth metal cations, analuminum atom, and an ammonium cation; and, n is a whole number equal tobetween 1 and 3, equal to the valence of Me.
 2. The composition of claim1 wherein said first salt is selected from the group consisting ofK₂HPO₃, KH₂PO₃, K₃PO₃, (NH₃) H₂PO₃, and (NH₃)₂HPO₃; and said second saltis selected from the group consisting of K₂HPO₄, KH₂PO₄, and K₃PO₄. 3.The composition of claim 1 wherein said composition is in an aqueoussolution, wherein each said first and second salt is present in solutionfrom about 20 millimole to about 5% vol./vol.
 4. The composition ofclaim 1 wherein said first salt is equal to one part by weight and saidsecond salt is equal to between 0.001 and 1,000 parts by weight.
 5. Thecomposition of claim 1 wherein said composition prevents diseases causedby Phytophthora infestans species.
 6. The composition of claim 1 whereinthe plants are tomato and potato species.
 7. A method for preventing andcontrolling diseases caused by Phytophthora in plants, comprising: (a)forming a composition comprising an effective amount of a first salt ofthe formula:

and a second salt having the following formula:

where R₁ is selected from the group consisting of H, K, an alkyl radicalcontaining from 1 to 4 carbon atoms, halogen-substituted alkyl ornitro-substituted alkyl radical, an alkenyl, halogen-substitutedalkenyl, alkynl, halogen-substituted alkynl, alkoxy-substituted alkylradical, ammonium substituted by alkyl or hydroxy alkyl radicals; R₂ andR₃ are selected from the group consisting of H and K; Me is selectedfrom the group consisting of K, alkaline earth metal cations, analuminum atom, and an ammonium cation; and, n is a whole number equal tobetween 1 and 3, equal to the valence of Me; and, (b) applying asufficient amount of said composition at least once to the plant.
 8. Themethod of claim 7 wherein said first salt is selected from the groupconsisting of K₂HPO₃, KH₂PO₃, K₃PO₃, (NH₃) H₂PO₃, and (NH₃)₂HPO₃; andsaid second salt is selected from the group consisting of K₂HPO₄,KH₂PO₄, and K₃PO₄.
 9. The method of claim 7 wherein said first salt isK₂HPO₃ and said second salt is K₂HPO₄.
 10. The method of claim 7 whereinsaid composition comprises an aqueous solution, wherein each said firstand second salt being present in solution from about 20 millimole toabout 5% vol./vol.
 11. The method of claim 7 wherein said first salt isequal to one part by weight and said second salt is equal to between0.001 and 1,000 parts by weight.
 12. The method of claim 7 wherein saidcomposition can be applied to the plant prior to or after infection bythe Phytophthora organism.
 13. The method of claim 7 wherein saidcomposition is used to prevent infection by Phytophthora infestans. 14.A composition for preventing and controlling diseases in plants causedby Phytophthora, whereby said composition comprises an effective amountof at least a first salt having the following formula:

and a second salt having the following formula:

where R₁ is selected from the group consisting of H, K, an alkyl radicalcontaining from 1 to 4 carbon atoms, halogen-substituted alkyl ornitro-substituted alkyl radical, an alkenyl, halogen-substitutedalkenyl, alkynl, halogen-substituted alkynl, alkoxy-substituted alkylradical, ammonium substituted by alkyl or hydroxy alkyl radicals; R₂ andR₃ are selected from a group consisting of H and K; Me is selected froma group consisting of K, alkaline earth metal cations, or aluminum atom;ammonium cation; and n is a whole number from 1 to 3, equal to thevalence of Me.
 15. The composition of claim 14 wherein said compositioncomprises an aqueous solution, wherein each said first and second saltbeing present in solution from about 20 millimole to about 5% vol./vol.16. The composition of claim 14 wherein said first salt is selected fromthe group consisting of K₂HPO₃, KH₂PO₃, K₃PO₃, (NH₃)₂ HPO₃, and (NH₃)H₂PO₃; and said second salt is selected from the group consisting ofK₂HPO₄, KH₂PO₄, K₃PO₄ (NH₃)₂HPO₃, and (NH₃) H₂PO₃.
 17. The compositionof claim 14 wherein the amount of said first salt is one part by weightand the amount of said second salt is between 0.001 and 1,000 parts byweight.
 18. A composition for preventing diseases in plants caused byPhytophthora-Phycomycetes, Ascomycetes, and other fungal and bacterialdiseases whereby said composition comprises an effective amount of atleast a first salt having the following formula:

and a second salt having the following formula:

where R₁ is selected from the group consisting of H, K, an alkyl radicalcontaining from 1 to 4 carbon atoms, halogen-substituted alkyl ornitro-substituted alkyl radical, an alkenyl, halogen-substitutedalkenyl, alkynyl, halogen-substituted alkynl, alkoxy-substituted alkylradical, ammonium substituted by alkyl or hydroxy alkyl radicals; R₂ andR₃ are selected from the group consisting of H and K; Me is selectedfrom the group consisting of K, alkaline earth metal cations, analuminum atom, and an ammonium cation; and, n is a whole number equal tobetween 1 and 3, equal to the valence of Me, whereby said first salt andsaid second salt, when combined, have a synergistic effect so thatdisease control is at least 100% greater than the additive affect of thecombined salts.